FIG. 9 chows a conventional boring machine 100 for carrying out a boring process to a large-sized work. The boring machine 100 comprises a guide, rail 120 linearly extending in one direction, a main part 130 slidably mounted on the guide rail 120, a sleeve 140 extending from the main part 130 in a plane substantially parallel to the guide rail 120, and a rotatable face plate 160 mounted at a distal end of the sleeve 140.
A cutting tool 165 is mounted on the rotatable face plate 160. When the rotatable face plate 160 is rotated, the cutting tool 165 is also rotated, so that a boring process is carried out. Another cutting tool 158 is mounted on the rotatable face plate 160, on the opposite side of the cutting tool 165, in order to achieve a weight balance.
In addition, the cutting tool 165 is mounted on the rotatable face plate 160 preferably via a U-axis controlling mechanism which can extend and contract in a radial direction of the rotatable face plate 160. In this case, it is easy to machine a surface perpendicular to an axis of a boring hole, in a desired manner.